This invention relates to optical rangefinders, and, more particularly, to an optical rangefinder with a distance scale which is read through the viewfinder and a system for adjusting or calibrating the scale.
Rangefinders which operate on the principal of optical triangulation are well known. For example, U.S. Pat. No. 3,817,621 describes an optical rangefinder which includes an eyepiece in the rear of a housing and two spaced optical elements in the front of the housing for projecting images from a remote object to the eyepiece. One of the optical elements is a beamsplitter which permits some of the light from the remote object to pass directly to the eyepiece and reflects the remainder of the light. The other optical element is a mirror which reflects light from the remote object to the beamsplitter where some of the light is reflected to the eyepiece. One of the optical elements is adjusted in a pivotal manner relative to the other until the two images are coincident, and a distance scale which is operatively connected to the adjusting mechanism provides a readout of the distance of the remote object. However, the distance scale is read through a separate window in the housing, and the user cannot read the distance scale through the viewfinder.
U.S Pat. No. 2,058,484 describes a rangefinder in which a distance scale is mounted on the indirect window and moves with the adjusting mechanism. Light from the remote object and the scale is reflected simultaneously from the indirect window to the eyepiece, and there is no calibration mechanism which permits the scale to be calibrated in order to provide accurate readings.